The subject invention pertains to cosmetic compositions containing a compound represented by the formula ##STR2## wherein R is sodium, potassium or ammonium and x is 1 or R is aluminum and x is 3.
The compounds of formula I are known compounds and are disclosed in British Pat. No. 957,458 as being useful in cosmetic preparations such as hair lotions, skin creams and the like.
The compounds of formula I, which may be written in a tautomeric form, i.e. "thione-form," are very susceptible to oxidation, particularly in high dilution. Oxidation of the compounds of formula I in solution results in the formation of 2,2'-dithiodipyridine-1,1-dioxide. This susceptability to oxidation has caused problems with the formulation of the compounds of formula I into cosmetic preparations. Since such preparations are normally not stored in a dark place or with the exclusion of light, photochemical oxidation of the compounds of formula I when incorporated therein also presents a significant problem.
The problem of how to stabilize cosmetic preparations containing the compounds of formula I against photodecomposition has been solved in accordance with the present invention by the incorporation therein of an effective amount of N-acetylcysteine. The stabilizing effect of N-acetylcysteine on preparation containing the compounds of formula I is considered unexpected, since N-acetylcysteine exhibits no light absorption over the entire range of the solar spectrum.